Process for forming backed microporous sheet

ABSTRACT

Process for forming a microporous polyurethane body backed with fibrous sheet material in which process a body of an emulsion is prepared of which the discontinuous phase is a volatile nonsolvent liquid and the continuous phase is a liquid polymeric material which sets through reaction to solid condition, the liquid emulsion is formed as a layer and reacted under conditions preserving the uniformity of the emulsion to pressure flowable stage having a pre-gel structure which will prevent sinking in of a fibrous sheet material and fibrous sheet material is laid on the layer and pressed into engagement with it to cause the emulsion to adhere to the fibrous sheet and to conform to irregularities. The reaction is continued to solidify the emulsion in firmly adherent relation to the fibrous sheet and the volatile liquid is removed from the solidified emulsion.

United States Patent 1 1 Day [451 Feb. 19,1974

[ PROCESS FOR FORMING BACKED MICROPOROUS SHEET [75] Inventor: John T.Day, Manchester, Mass.

[7 3] Assignee: USM Corporation, Boston, Mass.

[22] Filed: Sept. 13, 1972 [21] Appl. No.: 288,563

Primary Examiner-Edward G. Whitby Attorney, Agent, or Firm-Benjamin C.Pollard [57] ABSTRACT Process for forming a microporous polyurethanebody backed with fibrous sheet material in which process a body of anemulsion is prepared of which the discontinuous phase is a volatilenon-solvent liquid and the continuous phase is a liquid polymericmaterial which sets through reaction to solid condition, the liquidemulsion is formed as a layer and reacted under conditions preservingthe unifonnity of the emulsion to pressure flowable stage having apre-gel structure which will prevent sinking in of a fibrous sheetmaterial and fibrous sheet material is laid on the layer and pressedinto engagement with it to cause the emulsion to adhere to 'the fibroussheet and to conform to irregularities. The reaction is continued tosolidify the emulsion in firmly adherent relation to the fibrous sheetand the volatile liquid is removed from the solidified emulsion.

10 Claims, 3 Drawing Figures PROCESS FOR FORMING BACKED MICROPOROUSSHEET FIELD OF USE, BACKGROUND AND PRIOR ART RELATIVE TO THE INVENTIONThis invention relates to an improved process for making a microporouspolyurethane body backed with fibrous sheet material.

In the US. Pat. of John J. McGarr, No. 3,5Sl,364, dated Dec. 29, 1970,entitled Processes for Making Microporous Polyurethane Bodies EmployingNon- Boiling Liquid Alkyl Ethers or Liquid Aliphatic Hydrocarbons, thereis disclosed a process in which an emulsion formed in which thediscontinuous phase is drop lets of a nonsolvent liquid and thecontinuous phase is a reactive polymeric material convertible throughreaction to a tough, solid, resilient film-forming condition. Theemulsion is formed into a body of desired shape and reacted to solidifythe reacted material with the droplets of non-solvent liquid held in thesolidified body. The non-solvent liquid of the droplets is removed fromthe solidified body leaving spaces constituting openings or pores.

The patent also discloses procedure in which a layer of reactiveemulsion is formed on a casting surface and a porous fibrous sheet islaid on the free surface of the layer while the layer is still in liquidcondition before solidification through reaction. As noted in thatpatent, conditions adjacent the surface of the layer may cause thesurface to be less porous than other portions of the layer.

SUMMARY OF THE INVENTION It is an object of the present invention toprovide a process for forming a microporous polyurethane body integrallyunited to a fibrous backing in which process improved uniform porosityis secured in the polyurethane material To this end and in accordancewith a feature of the present invention liquid reactive urethaneemulsion is cast as a layer on a casting surface with the surfaceopposite the casting surface stabilized until development of limited gelstructure and thereafter a fibrous sheet is laid on the surface of thestill pressure flowable emulsion and pressed into intimate engagementwith the emulsion.

I have discovered a process for forming a microporous sheet with afibrous backing in which overall uniform porosity of the microporoussheet is secured by casting a layer of an emulsion of which the liquidcontinuous phase is based on a polymeric material reactive to solidresilient condition and the dispersion phase is non-solvent liquiddroplets and maintaining the layer of emulsion undisturbed with itssurfaces covered during an initial period for development of apreliminary gel structure in which the layer has sufficient integrity toallow separation of a cover from the cast surface without distortion ofthe surface but the emulsion is flowable under pressure. At this point,a cover is removed from a surface of the layer and a fibrous sheet ispressed into intimate engagement with the layer. The reaction iscontinued to solidify the emulsion in firmly adherent relation to thefibrous sheet and the volatile liquid is removed from the solidifiedemulsion.

BRIEF DESCRIPTION OF THE DRAWING Reference is made to the attacheddrawings forming part of the disclosure of the present case in which:

FIG. 1 is a diagrammatic elevational view of an arrangement of apparatussuitable for practicing the invention;

FIG. 2 is a fragmentary sectional elevational view taken on the lineIl-II of FIG. 1 of a cast layer with casting surfaces and cover sheet asmay be formed on the apparatus of FIG. 1;

FIG. 3 is a fragmentary sectional elevational view of a cast layer withcasting surface and fibrous backing layer taken on the line III-Ill ofFIG. 1;

DESCRIPTION OF THE PREFERRED EMBODIMENT Pores or passageways in a bodyof resilient polymeric material in the present process are secured bysolidifying a reactive emulsion in which the dispersed phase is dropletsof non-solvent liquid and the liquid continuous phase comprises reactivepolymeric material, and removing the non-solvent liquid from thesolidified con tinuous phase leaving the spaces previously occupied bythe non-solvent liquid as pores and passageways. Reactive emulsions foruse in the present process may be similar to the formulae used in theearlier filed patent of McGarr, referred to above.

Forming the combined microporous layer and fibrous backing according tothe present invention involves providing a layer of the emulsion on acasting surface, directly disposing a cover sheet on the layer,maintaining the layer under conditions which do not disrupt the layer ofemulsion during an initial period in which the emulsion thickens throughreaction to develop a preliminary gel structure and through cooling ofthe emulsion and, at this point, removing the cover sheet and pressing afibrous sheet into intimate engagement with the layer. Thereafter, thereaction to solidify the emulsion in firmly adherent relation to thefiber sheet is carried out and the volatile liquid is removed from thesolidified emulsion leaving a uniform microporous layer integrallyunited with the fibrous sheet backing.

The process will be described in connection with an apparatus suitablefor the manufacture of the backed microporous sheet; but it is to beunderstood that the procedures may be carried out by hand or with othersuitable apparatus.

Referring to FIG. 1, polymeric reactants and nonsolvent organic liquidto be mixed and emulsified are introduced through inlets 10 into themixer-emulsifier 12 where they are acted on by the agitating blades 14.The resulting emulsion is discharged through nozzle 16 and deposited asa layer 18 on the casting surface 20.

In the form shown, the casting surface 20 is a release sheet suppliedfrom a roll 22. The release sheet casting surface 20 is moved, suitablyon conveyor 24 or on a slip plate (not shown) beneath the nozzle 16which deposits the emulsion on successive portions of the sur face.Where the deposited emulsion is to be cooled, suitable cooling means maybe provided such as a chilled plate (not shown) beneath the sheetcasting surface 20 carrying the layer 18 of emulsion,

A flexible cover sheet 26 from the roll 28 is laid down on the emulsioncarried by the casting surface. Preferably, this is done by feeding thecover sheet 26 around the curved member 30 which brings the cover sheetin contact with the edge of the nozzle 16 so that in effect, the releasesheet 20 and cover sheet 26 with edge strips 32 at the edges of therelesase sheet 20 constitute a continuation of the nozzle to provideback pressure across the nozzle proper and effectively to eliminateshear movement in the emulsion layer 18. As shown in FIG. 2, the nozzle16 may be so designed that all portions of the emulsion have similartime and temperature histories at the time the emulsion leaves thenozzle proper and enters between spaced moving webs. The contactingsurface of the cover sheet 26 preferably carries or provides a materialgiving a low adhesion interface between cover sheet 26 and emulsionlayer 18 to minimize separational stress when the cover sheet is laterremoved and to insure that the adhesion of the layer 18 to cover sheet26 is less than its adhesion to casting surface 20. Thus, the coversheet may be wet with an inert liquid, non-solvent for the continuousphase of the emulsion. This may be one of the liquids useful as thediscontinuous phase. Alternatively, the cover sheet may be dusted with apowder not readily wet by the continuous phase or a gas or liquidinterface may be interposed between the cover sheet 26 and the emulsionlayer 18 as by using a permeable cover sheet and forcing the gas orliquid through the cover sheet. The cover sheet need not move with theemulsion in this case. The deposited emulsion is carried alongundisturbed after leaving the nozzle with the surfaces of the emulsionlayer 18 protected by the cover sheet 26, release sheet 20 and edgestrips 32.

The cover strip 26 is then drawn up from the surface of the emulsionlayer 18 around the roller 34 and is wound up on the roll 36. Thelocation of the roller 34 which draws the cover sheet 26 away from thelayer 18 is determined by the requirement of maintaining back pressureto give proper flow characteristic to the nozzle and by the rate atwhich the emulsion thickens and reaches the preliminary gel stageallowing the cover sheet to be withdrawn without disruption of the layer18.

After the cover sheet is withdrawn and after any further time dwell, ifneeded, for additional thickening of the emulsion to prevent undesiredsinking in of the backing, fibrous backing material 38 is pressed downonto the emulsion layer 18. The backer materials may be practically anyfabric which does not have chemical activity which would interfere withtheongoing action and which does not carry a surface active materialwhich would influence the surface active balance of the emulsion. Thesematerials include woven and nonwoven fabrics. The nonwoven fabrics maybe needle punched, knit stitched, impregnated or resin bonded. Thefabrics may be napped or unnapped. A very useful material includesnapped and sheared sateen but plain sateen, cotton drill and other weaveknits may be used. Backers have been made of rayon, polyester,polypropylene, nylon, cotton filaments and other fibers andcombinations. It has been found desirable to pre-wet the backingmaterial 38 with an inert liquid non-solvent for the continuous phase,e.g., liquids suitable for the disperse phase of the emulsion, beforeassociating the backing material with the emulsion layer. This is doneconventionally. by dipping the fabric in the liquidand passing itthrough a wringer prior to winding it into the roll 40. As shown in thedrawing, the fibrous backing 38 from the roll 40 is fed around the.roller 42 which presses it against the surface of the emulsion layer 18to form the assembly shown in FIG. 3.

After the fibrous backing has been pressed onto the surface of theemulsion layer, the composite is carried along to allow the reaction toproceed to a point at which the structure of the emulsion layer 18 isstable and resistant to harm by handling. At this point, the compositeof solidified emulsion layer 18 and fibrous backing 38 may be strippedfrom the release sheet 20 for further treatment such as curing andremoval of the non-solvent liquid of the droplets.

Reactive materials for use in the solidifiable continuous phase arethose for forming elastomeric polyurethane or polyurea reactionproducts, both of which are hereafter referred to as polyurethanes, andare selected on the basis of their ability to provide toughness,flexibility, hardness and other physical properties required in thefinal product. The reactive material may be a one shot" mixture of anorganic compound having at least two active hydrogens such as apolymeric polyol, e.g., polyalkylene ether polyol and/or polyesterpolyol with a reactive compound having at least two reactive -NCOgroups, e.g., a polyisocyanate. Alternatively, there may be used aprepolymer system in which an -NCO terminated reaction product of apolyol with excess polyisocyanate is combined with chain extenders whichmay be polyhydroxy or polyamine or amino alcohol compounds having atleast two hydroxyl or amine groups providing active hydrogens forreaction with -NCO groups.

It has been found desirable to use polyol material or prepolymers whichat room temperature are solid or pasty. The term pasty refers toconsistency which may be very high viscosity or may be partially solidwhich is capable of permanent deformation or even flow under substantialpressure, but which does not allow rapid, effective intimate mixing withother reagents and with the non-solvent liquid component to form a freeflowing liquid emulsion with ordinary mixing and emulsifying equipmentsuch as a high shear propeller type mixer. These materials offer thespecial advantage that cooling of the emulsion after formation into alayer helps to thicken the emulsion layer to aid in resisting distortionwhen the cover sheet 26 is removed.

Polyols useful in the one shot mixture or for forming the reactiveprepolymer include substantially linear or only moderately branchedpolyether polyols, and substantially linear or moderately branchedpolyester polyols from the condensation of polybasic acids, e.g., adipicacid, sebacic acid, azelaic acid, dimerized linoleic acid and otheraliphatic and aromatic dibasic acids with polyols such as butane diol,ethylene glycol, propylene glycol and the like. Castol oil is also asuitable polyol for making a prepolymer. Controlled portions of polyolsor polybasic acids having more than two reactive -OH or -COOl-l groupsmay be included in l the compositions reactive to form polyester polyolsto persed droplets until the coating at least partially solidi fiesaround the droplets and is removed thereafter leaving open spaces andpores. Removal is effected without expansion of the solidified body.Suitable liquids may readily be selected by a chemist on the basis ofthe known physical properties of liquids. Any liquid havingsubstantially non-solvency and non-reactivity with the polymericmaterial together with suitable volatility characteristics may be used.Normally liquid aliphatic hydrocarbons including petroleum hydrocarbonfractions, particularly those commercially available as mineral spirits,petroleum naphtha and kerosene which are largely or completely aliphaticin composition are generally preferred because of their low cost andsatisfactory behavior in the composition; but other substantially inertorganic liquids such as liquid alkyl ethers, e.g., amyl ether anddibutyl ether and liquid halogenated hydrocarbons, preferablyhalogenated aliphatic hydrocarbons such as chlorodecane,tetrachloroethylene and tctrachlorodifluoroethane may be used. To avoidpremature evaporation from the body of emulsion so that it can serve itsspace filling function until it has solidified, the pore-forming liquidis chosen to have a boiling point above the selected mixing and reactiontemperatures and should preferably have a boiling point of at leastabout 100C. and preferably at least 130C. to allow use of temperaturesgiving a desirable fluidity and rate of reaction of the polymericmaterial. On the other hand, the liquid will be chosen with low enoughboiling point for removal without heat injury to the solidified body orto a base with which it may be associated. Thus, the liquid shouldordinarily not contain substantial quantities of high boiling or lowvolatility components, and preferably at least 90 percent of thecomponents-should boil at temperatures below 232C. It is to beunderstood that other means than evaporation, e.'g., extraction may beused to remove high boiling or low volatility liquid and in such casesthe upper limit of boiling point does not apply.

The extent of heating of the reactive polymeric material needed to bringthe material to a suitably low viscosity, which may he of the order of6,000 centipoises, for emulsion forming, depends on the properties ofthe material. Higher melting point and higher molecular weight reactivepolymeric materials require higher temperatures. Polymeric materialsgiving the desired improvements in retention of uniform dropletdistribution of the emulsion in layer form call for heating to atemperature of at least about 50C.

Dispersion of droplets of the pore-forming liquid in the heated liquidbody of reactive polymeric material to form an emulsion in which thereactive polymeric material is the continuous phase, is effected byvigorous agitation during the course of addition of the poreformingliquid to the body of polymeric material. Surface active agents areuseful to aid in dispersing the liquid in the polymeric material and tocontrol the stability of the resulting emulsion. Preferred emulsifyingagents have included anionic and non-ionic surface active agents such ascommercially available silicone emulsifiers, polyoxyalkylene ethers suchas a commercial polypropoxy/polyethoxy ether, partial long chain fattyacid esters and the polyoxyalkylene derivatives of such esters, alsosulfuric acid esters of long chain fatty alcohols, etc.

The amount of pore-forming liquid dispersed will vary with the desiredporosity of the final product and may vary from as low as, based onparts by weight, 25 parts of the liquid to 100 parts of the polymer upto as high as 300 parts of the liquid to 100 parts of the polymermaterial. It is preferred to use from about 60 parts to about 200 partsof liquid to parts of the polymeric material. It is desirable that themechanical conditions of dispersion of the liquid and the polymer becontrolled to form very small droplet sizes of which the majority willbe in the range of from 0.001 mm. to about 0.03 mm. in diameter.

Reaction of the polymeric material to higher molecular weight solidcondition is brought about and controlled by the time and temperatureconditions of bringing together of the reactive components and/or by theintroduction of catalyst. In the one step process in which a polymericpolyol such as the polyester polyol or polyether polyol is reacted witha polyisocyanate, mixing and emulsiflcation involves bringing togetherthese materials together with the liquid to be dispersed and a catalysteffective to control the reaction rate.

In the two step process, an -NCO terminated prepolymer prepared from apolymeric polyol such as an hydroxyl terminated polyether or polyesterand a polyisocyanate, the pore forming liquid, and chain extendersreactive with the prepolymer to give higher molecular weight materialsare combined and emulsified, with the prepolymer material forming thecontinuous phase. Chain extenders effective to increase the molecularweight of the prepolymer are compounds having two or more activehydrogen atoms such as p,p' methylenedianiline, 4,4'-methylene-bis-(2,-chloroaniline), trimethylolpropane, m-

phenylediamine, 1,4 butanediol and triethanolamine.

Cover sheet 26 (see FIG. 1), which may be wet with an inert non-solventliquid is laid down on the surface of the deposited emulsion layer 18opposite the casting surface 20 as the layer is formed, or promptlyafter it is formed. The cover may be a release sheet such as a papersheet carrying a non-adhesive deposit for example, of silicone,polytetrafluoroethylene, polychlorotrifluoroethylene, wax, polyethyleneor polypropylene or may be a non-adhesive supported or unsupported resinor elastomer sheet. The cover cover sheet 26 is preferably flexible forconvenience in handling and may be laid down on the emulsion layer 18 byhand or by any of the known devices for laying a sheet down smoothly ona surface.

With the cover sheet 26 in place, the reaction of the polymeric materialrapidly produces a preliminary gel structure in which the emulsion hassufficient stability that the stripping of the cover sheet does notdisrupt of distort the surfaces of the emulsion from which it isstripped.

Control of the reaction to insure reaching the desired partial gellationby the time the cover sheet is stripped off may be controlled by suchfactors as temperature, catalyst and rate of speed of the conveyor. Theknown catalysts for urethane reactions may be used. It has been foundparticularly desirable to use a catalyst having an induction periodduring which no important physical changes occur in the reaction mixtureso that in the present process mixing and deposition as a layer 18between the casting sheet 20 and the cover sheet 26 occurs beforepreliminary gellation has begun, while at the same time, once theinduction period has passed, the catalyst is effective to complete thecure of the urethane in a minimum time. As the catalyst having an in-'duetion period there may be used mercuric salts of aliphatic and/oraromatic carboxylic acids. Among such curic isobutyrate, mercuricpropionate, mercuric octoate, mercuric oleate, mercuric stearate,mercuric oxalate, mercuric adipate, mercuric benzoate, mercuricanthranilate, phenyl mercuric chloride, phenyl mercuric nitrate,mercuric naphthenate and phenyl mercuric oleate. This catalyst may beused in amount of from about 0.01 percent to about 0.4 percent,preferably about 0.10 percent by weight based on the weight of theresin.

With this catalyst there may be used a catalyst effective to cause rapidbut limited initial build up in viscosity or precursor gellation. Suchcatalysts may include triethylene diamine, N,N,NN tetramethylene butanediamine, dibutyl tin dilaurate, stannous octoate and lead naphthenate.These materials will ordinarily be used in proportion of from about0.002 percent to about 0.7 percent by weight based on the weight of theresin.

The use of a rapid catalyst such as a tin compound is believed to reducethe desparity between the rate of reaction of the isocyanate and thepolyester or polyether polyol on the one hand and the rate of reactionbetween the isocyanate and the short chain diol modifier on the otherhand and to give best product quality. Rapid catalysts are alsoeffective to speed up the reaction between the isocyanate with hydroxylterminated compounds so that the tendencies for the isocyanate to beextruded into the inert liquid of the discontinuous phase is reduced.The rapid reaction also enables the cover sheet 26 to be removed in avery brief space and the combination of rapid catalyst and catalysthaving an induction period operates so that the composite of fibrousbacking sheet 38 and solidified emulsion layer 18 will reach a conditionin which it can be handled in a minimum .time. It is to observed thatthe tin catalyst tends to give immediate action and that there isevidence that the mercury catalyst slows the action of the tin catalystsothat time is available for forming the emulsion layer.

The following'examples are given to aid in understanding the inventionbut it is to be understood that the invention is not restricted to thematerials, proportions or procedures of the examples.

EXAMPLE 1 130 grams (0.0844 mols) of -NCO terminated prepolymer preparedby reaction of p,p-diphenyl methane diisocyanate and hydroxyl terminatedpolybutylene adipate in a mol ratio of 2: 1 resulting prepolymer havingmolecular weight of 1,540, and being solid at room temperature wasliquefied and degassed at 100C. and mixed with 3.9 grams of anemulsifier defined as blended polypropoxy/polyethoxy ether having anhydroxyl number of which is a solid at C. and the mixture was'brought toatemperature of 100C. 148 cc. of a liquid, paraffinic hydrocarbonmixture (boiling range 346F. to 405F.) was added slowly to the heatedmixture of polybutylene adipate and the emulsifier with vigorousagitation to form an emulsion with the hydrocarbon as the internalphase. 7.75 grams (0.0860 mols) of 1,4 butane diol, about 7 grams ofmethyl isobutyl ketone and about 0.26 grams of an organosilicone blockcopolymer surfactant were added and mixed in. The resulting reactiveemulsion was at a temperature of 100 C. and was supplied through anozzle to the space between a casting sheet of release paper and anupper cover sheet of release paper, the surface of the cover sheethaving been wet with the liquid paraffinic hydrocarbon mixture formingthe internal phase of the emulsion, the layer of emulsion being 0.08inch in thickness. The layer was carried by the cover sheet betweencooled aluminum plate maintained at a temperature of 75C. After 7minutes, the cover sheet was stripped from the layer of emulsion and thetemperature of the emulsion layer was increased 100C. After 30 minutesat this temperature a napped and sheared cotten sateen backer which hadbeen wet with naphtha and squeezed to remove excess naphtha was laid onthe surface of the emulsion. The assembly was held in a closed conditionwhich inhibited naphtha evaporation and was stripped from the castingsheet and held'in an oven at 100C. for 24 hours to complete curing ofthe layer and evaporation of the hydrocarbon layer of the compositesheet. An excellent backed microporous polyurethane sheet material wasobtained.

EXAMPLE 2 An emulsion of the prepolymer, emulsifier and liquidparaffinic hydrocarbon mixture, butane diol and surfactant was preparedas in Example 1 with the addition of a commercial tin catalyst for thereaction of isocyanate and hydroxyl in amount of 20 parts of catalystper million parts of polyurethane and the emulsion was supplied at atemperature of 60C. between a casting sheet and a cover sheet as a layerabout 0.02 inch in thickness. The emulsion layer, with the casting andcover sheets in place, was passed in contact with cooled aluminum platesmaintain at a temperature of 45C. The cover sheet was stripped off after15 seconds and the layer of emulsion was brought to C. for 1 minute. Atthis-point, a nonwoven polyester fiber sheet was laid on the exposedphase of the emulsion layer and the assembly was brought to 100C.Afte'r'8 minutes at 100C., the backer and solidified emulsion layer werestripped from the casting sheet and air dried at 100C. for 30 minutes.The resulting sheet was a fine microporous polyurethane backed sheetmaterial.

EXAMPLE 3' The procedure of Example 2 was repeated; but there was alsoincluded 1,500 parts per million of a mercury salt of a carboxylic acidas well as the tin catalyst. The emulsion was supplied between thecasting sheet and the cover sheet at a temperature of C. and thecomposite of casting sheet emulsion layer and cover sheet were passedbetweencooled aluminum plates maintained at 35C. After 25 seconds thecover sheet was peeled off and the emulsion layer was brought to atemperature of C. After 4 minutes at this temperature a stitch bondedcontinuous filament polyester nonwoven fibric was laid on the emulsionlayer. This assembly was held at 1 15C. for 5 minutes in a closedchamber which inhibited evaporation and was then stripped from thecarrier sheet and pressed in an oven at 100C. for 25 minutes toevaporate the liquid hydrocarbon and complete the cure of thepolyurethanefof the emulsion layer.

' Having thus described my invention what I claim as new and desire tosecure as Letters Patent of the United States is; 1

l. The process of forming a microporous sheet of solid polyurethanecomprising the steps-of casting an emulsion of fine droplets of avolatile organic liquid as the internal phase in a continuousphasecomprising reactive material convertible through reaction to solidified,resilient, film-forming condition, said reactive material comprising amixture of an organic compound providing at least two reactive -NCOgroups per molecule and an organic compound having at least two activehydrogens per molecule for reaction with said -NCO groups, said organicliquid being substantially non-solvent for and non-reactive with saidreactive material, being immiscible in said continuous phase and beingpresent in amount from about 60 percent to about 300 percent by weightbased on the weight of the reactive material, reacting said material ata temperature below the boiling point of said liquid so that the liquidnever boils to cause the emulsion to gel and solidify with said dropletsheld in the solidified material and removing said liquid withoutexpanding the solidified material leaving pores and discontinuities inthe solidified material to constitute passageways for air and vapor, theimprovement which comprises forming a layer of the liquid emulsion,reacting the materials of the continuous phase of the emulsion underconditions preserving the uniformity of the emulsion to a thickenedpressure flowable stage having a pre-gel structure which will preventsinking in of a fibrous sheet material, bringing fibrous sheet materialinto intimate engagement with said layer to cause the emulsion to adhereto the fibrous sheet, completing said reaction to form a stable solidbody and removing said volatile organic liquid from the solidifiedmaterial.

2. The process of forming a microporous sheet of solid polyurethane asdefined in claim 1 in which said layer of emulsion is formed betweenspaced release surfaces promptly after formation while said emulsion isliquid and in which one of said release surfaces is stripped from saidlayer of emulsion when said emulsion has thickened to a stage where theemulsion is no longer freely liquid and maintains undeformed the surfacefrom which the release surface is stripped.

3. The process of forming a microporous sheet of solid polyurethane asdefined in claim 2 in which said layer of emulsion is formed betweensaid release surfaces and is cooled to aid in thickening the emulsionprior to stripping one of said release surfaces from the layer ofemulsion.

4. The process of forming a microporous sheet of solid polyurethane asdefined in claim 3 in which at least one of said reactive materials ispolymeric and is solid or pasty at room temperature, said solid or pastyreactive material is heated to bring it to free fluid state for mixingwith other reactive materials, said immiscible liquid is emulsified withsaid reactive materials while said solid or pasty reactive material isin heated state, and in which said layer of emulsion is formed betweensaid release surfaces while in heated condition.

5. The process of forming a microporous sheet of solid polyurethane asdefined in claim 2 in which said reactive material comprises a member ofthe group consisting of mixtures of at least one polymeric polyetherpolyol or one polyester polyol, an organic compound having at least 2reactive -NCO groups per molecule and a diol chain extender having from2 to 10 carbon atoms and a mixture of at least one prepolymer fromreacting stoichiometric excess of an organic compound having at least 2reactive -NCO groups per molecule with a polymeric polyether polyol,polyester polyol and a diol chain extender having from two to 10reactive material is heated to bring it to freely fluid state for mixingwith other reactive materials, said immiscible liquid is emulsified withsaid reactive materials while said solid or pasty reactive material isin heated state and in which said layer of emulsion is formed be tweensaid release surfaces while in heated condition and is cooled to aid inthickening the emulsion prior to stripping one of said release surfacesfrom the layer of emulsion.

7. The process of forming a microporous sheet of solid polyurethane asdefined in claim 2 in which said emulsion is deposited promptly afterformation while in freely fluid condition between spaced sheets ofrelease material moving at the same rate and maintained in spacedrelation a distance corresponding to the desired thickness of saidmicroporous sheet material, progressively stripping one of said releasesurfaces from said layer of emulsion when said emulsion has thickened toa stage where the emulsion is no longer freely liquid and maintainsundeformed the surface of the emulsion from which the release surfacewas stripped, progressively laying down a fibrous sheet material on saidlayer of emulsion when said emulsion has gelled to a stage at which thefibrous sheet material will not sink into said layer of its own weight,completing the reaction of the reactive materials of said emulsion toconvert said layer to resilient film-forming condition combined infirmly adherent relation to said fibrous sheet and thereafterprogressively stripping the combined fibrous sheet material and reactedemulsion layer from the remaining release sheet.

8. The process of forming a microporous sheet of solid polyurethane asdefined in claim 6 in which said emulsion is deposited promptly afterformation while in freely fluid condition between spaced sheets ofrelease material moving at the same rate and maintained in spacedrelation a distance corresponding to the desired thickness of saidmicroporous sheet material, progressively stripping one of said releasesurfaces from said layer of emulsion when said emulsion has thickened toa stage where the emulsion is no longer freely liquid and maintainsundeformed the surface of the emulsion from which the release surfacewas stripped, progressively laying down a fibrous sheet material on saidlayer of emulsion when said emulsion has gelled to a stage at which thefibrous sheet material will not sink into said layer of its own weight,completing the reaction of the reactive materials of said emulsion toconvert said layer to resilient film-forming condition combined infirmly adherent relation to said fibrous sheet and thereafterprogressively stripping the combined fibrous sheet material and reactedemulsion layer from the remaining release sheet.

9. The process of forming a microporous sheet of solid polyurethane asdefined in claim 8 in which material is supplied at the surface of oneof said release sheets providing a low adhesion interface between saidrelease sheet and said emulsion.

10. The process of forming a microporous sheet of solid polyurethane asdefined in claim 9 in which said release sheet is a flexible cover sheetof release material which is wet with inert non-solvent liquid at thesurface which will contact said layer of emulsion.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.3,793,102 Dated February 19, 1974 lnven fl John T. Day

It is certified vthat error appears in the above-identified patent andthat said Letters Patent are hereby corrected as shown below:

Claim 1, first line, delete The and insert ...In the-- signed and sealedthis 30th day of'July 1971+.

(SEAL) Attest:

C. MARSHALL DANN McCOY M. GIBSON, JR. Attesting Officer Commissioner ofPatents

2. The process of forming a microporous sheet of solid polyurethane asdefined in claim 1 in which said layer of emulsion is formed betweenspaced release surfaces promptly after formation while said emulsion isliquid and in which one of said release surfaces is stripped from saidlayer of emulsion when said emulsion has thickened to a stage where theemulsion is no longer freely liquid and maintains undeformed the surfacefrom which the release surface is stripped.
 3. The process of forming amicroporous sheet of solid polyurethane as defined in claim 2 in whichsaid layer of emulsion is formed between said release surfaces and iscooled to aid in thickening the emulsion prior to stripping one of saidrelease surfaces from the layer of emulsion.
 4. The process of forming amicroporous sheet of solid polyurethane as defined in claim 3 in whichat least one of said reactive materials is polymeric and is solid orpasty at room temperature, said solid or pasty reactive material isheated to bring it to free fluid state for mixing with other reactivematerials, said immiscible liquid is emulsified with said reactivematerials while said solid or pasty reactive material is in heatedstate, and in which said layer of emulsion is formed between saidrelease surfaces while in heated condition.
 5. The process of forming amicroporous sheet of solid polyurethane as defined in claim 2 in whichsaid reactive material comprises a member of the group consisting ofmixtures of at least one polymeric polyether polyol or one polyesterpolyol, an organic compound having At least 2 reactive -NCO groups permolecule and a diol chain extender having from 2 to 10 carbon atoms anda mixture of at least one prepolymer from reacting stoichiometric excessof an organic compound having at least 2 reactive -NCO groups permolecule with a polymeric polyether polyol, polyester polyol and a diolchain extender having from two to 10 carbon atoms, and a catalystfavoring reaction of isocyanate radicals with the active hydrogens ofpolyester polyols or polyether polyols over reaction between saidpolyisocyanate and the active hydrogens of said chain extender.
 6. Theprocess of forming a microporous sheet of solid polyurethane as definedin claim 5 in which at least one of said reactive materials is polymericand is solid or pasty at room temperature, said solid or pasty reactivematerial is heated to bring it to freely fluid state for mixing withother reactive materials, said immiscible liquid is emulsified with saidreactive materials while said solid or pasty reactive material is inheated state and in which said layer of emulsion is formed between saidrelease surfaces while in heated condition and is cooled to aid inthickening the emulsion prior to stripping one of said release surfacesfrom the layer of emulsion.
 7. The process of forming a microporoussheet of solid polyurethane as defined in claim 2 in which said emulsionis deposited promptly after formation while in freely fluid conditionbetween spaced sheets of release material moving at the same rate andmaintained in spaced relation a distance corresponding to the desiredthickness of said microporous sheet material, progressively strippingone of said release surfaces from said layer of emulsion when saidemulsion has thickened to a stage where the emulsion is no longer freelyliquid and maintains undeformed the surface of the emulsion from whichthe release surface was stripped, progressively laying down a fibroussheet material on said layer of emulsion when said emulsion has gelledto a stage at which the fibrous sheet material will not sink into saidlayer of its own weight, completing the reaction of the reactivematerials of said emulsion to convert said layer to resilientfilm-forming condition combined in firmly adherent relation to saidfibrous sheet and thereafter progressively stripping the combinedfibrous sheet material and reacted emulsion layer from the remainingrelease sheet.
 8. The process of forming a microporous sheet of solidpolyurethane as defined in claim 6 in which said emulsion is depositedpromptly after formation while in freely fluid condition between spacedsheets of release material moving at the same rate and maintained inspaced relation a distance corresponding to the desired thickness ofsaid microporous sheet material, progressively stripping one of saidrelease surfaces from said layer of emulsion when said emulsion hasthickened to a stage where the emulsion is no longer freely liquid andmaintains undeformed the surface of the emulsion from which the releasesurface was stripped, progressively laying down a fibrous sheet materialon said layer of emulsion when said emulsion has gelled to a stage atwhich the fibrous sheet material will not sink into said layer of itsown weight, completing the reaction of the reactive materials of saidemulsion to convert said layer to resilient film-forming conditioncombined in firmly adherent relation to said fibrous sheet andthereafter progressively stripping the combined fibrous sheet materialand reacted emulsion layer from the remaining release sheet.
 9. Theprocess of forming a microporous sheet of solid polyurethane as definedin claim 8 in which material is supplied at the surface of one of saidrelease sheets providing a low adhesion interface between said releasesheet and said emulsion.
 10. The process of forming a microporous sheetof solid polyurethane as defined in claim 9 in which said release sheetis a flexible cover sheet of release material which is wet with inertnOn-solvent liquid at the surface which will contact said layer ofemulsion.